In recent years, conductive materials with positive temperature coefficients of resistance have been utilized in constructing a wide variety of self- or auto-regulated heating elements. The distinguishing characteristic associated with such conductive materials, known as PTC materials, is the substantial increase in resistance to conductivity which occurs as the material attains a certain temperature. This temperature (or temperature range, as the case may be) is usually designated the switching or anamoly temperature T.sub.s. Beyond the anamoly temperature T.sub.s, resistance in the material can become so high that any current flow through the material is effectively switched off. In practical terms, then, the anamoly temperature T.sub.s represents the maximum temperature obtainable by a PTC material in response to current flow therethrough, and heating elements constructed from PTC material consequently exhibit inherent self-regulation with respect to temperature.
Numerous PTC materials are ceramic in composition. Others may comprise conductive polymers of the type disclosed in U.S. Pat. No. 4,017,715 issued to Whitney et al on Apr. 12, 1977; U.S. Pat. No. 4,177,376 issued to Horsma et al on Dec. 4, 1979; and U.S. Pat. No. 4,177,446 issued to Diaz on Dec. 4, 1979. Despite the generally satisfactory performance of the PTC materials developed to date, however, some problems remain. Electrical faults, for example, can develop in either the heating circuit electrical connectors or in the PTC material itself, leading to excessive power dissipation and attendant catastrophic material failure accompanied by fire. Some means for monitoring the operation of conductive PTC heating elements in order to determine whether potentially dangerous faults are present would accordingly be of obvious benefit.